Some Effects of Competition and Density of Plants on Dry Weight Produced

Plant weights were compared for different levels of shoot density,root density, shoot interaction and root interaction. Also,the effects of these treatments on the shoot—root ratiowere studied. Plant weight increased with decreases in shootand root density. Generally, plants grown with shoots or rootsintermingled with those of adjacent plants had greater weightthan those grown with shoots or roots separated. Competitionwas detected only at the highest shoot density where adjacentplants with isolated roots had greater weight than adjacentplants with intermingled roots. This is hypothesized to be aphytotoxic effect due to shoot confinement. No effects of densityor intermingling on the shoot-root ratio were evident.     

Tamoxifen Inhibition of Ocular Melanoma Cell Attachment to Matrix Proteins

Tamoxifen plays a major role in the management of breast cancer in women and is currently used to a lesser extent in other neoplasias. Many of the pharmacological properties of tamoxifen are consistent with anti-estrogen activity, but it also has significant, although lesser, benefit in patients whose tumours are estrogen-receptor negative. We recently reported that murine B16 melanoma cell attachment to extracellular matrix proteins can be inhibited by calmodulin antagonists. In seeking a calmodulin antagonist that could be used clinically, we investigated tamoxifen, which is known to have calmodulin antagonist activity in vitro, and confirmed that it will inhibit murine melanoma cell attachment in vitro. In the current study, we examined the effect of tamoxifen on the attachment of human ocular melanoma cell lines to a range of extracellular matrix substrates to evaluate the potential relevance of calmodulin antagonists, including tamoxifen, to reducing metastatic spread of these tumours. We report that six ocular melanoma cell lines established from choroidal melanoma tumours showed rapid attachment to a range of substrates and that this attachment can be significantly reduced by an experimental calmodulin antagonist (J8) and by tamoxifen. In summary, we conclude that the ability of calmodulin antagonists, including tamoxifen, to inhibit ocular melanoma cell attachment to matrix proteins in vitro merits further investigation as it may offer another approach to reducing metastatic spread of these tumours.     

Mesophyll cells of C4 plants have fewer chloroplasts than those of closely related C3 plants

The evolution of C₄ photosynthesis from C₃ ancestors eliminates ribulose bisphosphate carboxylation in the mesophyll (M) cell chloroplast while activating phosphoenolpyruvate (PEP) carboxylation in the cytosol. These changes may lead to fewer chloroplasts and different chloroplast positioning within M cells. To evaluate these possibilities, we compared chloroplast number, size and position in M cells of closely related C₃, C₃–C₄ intermediate and C₄ species from 12 lineages of C₄ evolution. All C₃ species had more chloroplasts per M cell area than their C₄ relatives in high‐light growth conditions. C₃ species also had higher chloroplast coverage of the M cell periphery than C₄ species, particularly opposite intercellular air spaces. In M cells from 10 of the 12 C₄ lineages, a greater fraction of the chloroplast envelope was pulled away from the plasmalemma in the C₄ species than their C₃ relatives. C₃–C₄ intermediate species generally exhibited similar patterns as their C₃ relatives. We interpret these results to reflect adaptive shifts that facilitate efficient C₄ function by enhancing diffusive access to the site of primary carbon fixation in the cytosol. Fewer chloroplasts in C₄ M cells would also reduce shading of the bundle sheath chloroplasts, which also generate energy required by C₄ photosynthesis.